I guess what I've written below is a bit spoiler-ish regarding the threats in a certain area, and if you're concerned about that stuff, maybe stop reading.
I bought the fall damage ring from the cat in Majula and decided to explore that well. I ended up in a place called the Grave of Saints, and I'm immediately summoned as a grey phantom after I pass the bonfire. I had no idea what the hell that meant, but the dude on the other side sure did and backstabbed my ass as soon as I appeared in his world. The fight obviously didn't last long, and I ended up on the losing end.
So I figure this is some covenant crap similar to the one protecting the belfry in the Lost Bastille, and these guys are trying to farm unsuspecting idiots like myself. I'm a little wiser the next time I get summoned, and I immediately raise my shield and prepare for a fight. This time I trade a few blows with the guy until he starts backing off, and a swarm of rats comes at me while he takes a breather and heals himself. I managed to fend off the rats, but this asshole kept running deeper into the area (and tried to get me to aggro more rats) each time I got him on the ropes. Eventually a message pops up saying that time is up, and I get returned to my world with no reward and one Estus.
I explore a bit more and come upon another bonfire where I immediately rest and restock my Estus. Almost immediately after I get up, I get summoned for a third time. This guy has some poisoned fist and is a pushover. I easily get him to low health before he runs back to put some rats between us, and he heals up while I take out the vermin. Again, he tries to attack me, and I get him to within an inch of his life, and just like the previous guy, he starts running for safety deeper in the area. However, this time I had my fucking bow in my second slot and shot that asshole in the back before he could turn the corner.
Afterward, I cleared most of the area, met the rat king, and decided to warp out before getting summoned again. I'll probably go back later to PvP some more.